1. Slice beef into 2 cm / 3/4 in thick slices. Place each slice between two pieces of plastic wrap and pound with a mallet until 1/2 cm / 1/4 in thick.
2. Heat oil in a large frying pan over moderate heat. Add garlic, sugar, vinegar and Worcestershire sauce, cook for 1 minute.
3. Add beef slices and cook until just tender, about 1 minute each side. Remove beef with a slotted spoon and keep warm.
4. Bring pan juices to a boil, reduce heat and simmer until sauce thickens, about 1-2 minutes. Pour sauce over beef and sprinkle with sesame seeds. Serve immediately with a side salad if desired.